1. Field of the Disclosure
The disclosure relates generally to a photoresist coating composition and a method for forming a fine pattern using the same. More specifically, the disclosure relates to a photoresist coating composition comprising a water-soluble polymer and an aqueous solvent, and to a method for forming a fine pattern by reducing the size of the photoresist using the same.
2. Description of Related Technology
As the manufacturing technology of semiconductor devices has developed and the fields of application of memory devices has been extended, the development of lithography processes, (i.e., the development of photoresist materials, new exposure light sources, and light exposer technology) has been accelerated to develop memory devices with improved integration. However, since the resolution obtained by using commonly-used KrF and ArF light exposer is limited within 0.1 μm, it is difficult to form a fine pattern for manufacturing an integrated semiconductor device.
In order to form a conventional fine pattern, resist flow processes (hereinafter, referred to as “RFP”), processes using materials such as RELACS (resist enhancement lithography assisted by chemical shrink), and SAFIER (shrink assist film for enhanced resolution) produced by TOK Company have been introduced.
In the RFP, a photoresist pattern is formed by using an exposure process and a developing process, and then thermal energy is applied at above a glass transition temperature of the photoressist, so that the photoresist may flow thermally. The previously formed pattern has been gradually reduced by the supplied heat energy. As a result, a fine pattern is formed to have a small size required in an integrated process.
Referring to FIG. 1, an exposure process and a developing process are performed on a substrate 1 having an underlying layer 3, thereby obtaining a photoresist pattern 5. Then, thermal energy 7 is applied to the resulting structure at above a glass transition temperature of the photoresist for a predetermined time, which results in an inward thermal flow 9 of the photoresist to reduce the size of a contact hole or pattern.
Even when thermal energy is transmitted uniformly to the whole surface of photoresist in the RFP at a temperature above the glass transition temperature, the amount of photoresist flow is relatively larger in the lower portion than in the upper or middle portions. As a result, an overflowing phenomenon occurs such that the upper portion of the pattern becomes wider than the lower portion.
Since most of the photoresist sensitively reacts with the applied heat, the overflowing phenomenon most frequently occurs when the temperature regulation is mis-operated and the flowing time becomes longer than a predetermined value.
In order to reduce the overflowing phenomenon, temperatures of bake ovens for applying heat have been equalized or the baking time has been precisely regulated. However, although the above baking process is improved, the over flowing phenomenon is not reduced or eliminated.
According to the RELACS process, as shown in FIG. 2, an exposure process and a developing process are performed on a substrate 11 having an underlying layer 13, thereby obtaining a photoresist pattern 15. A RELACS material 17 is coated on the whole surface of photoresist, and then a developing process is performed on the resultant structure, by which a thermal process is performs on the resulting structure. As a result, a cross-linking reaction 19 is formed between the RELACS material 17 and the photoresist pattern 15 to reduce the size of a contact hole or a pattern.
According to the method using the SAFIER material, as shown in FIG. 3, an exposure process and a developing process are performed on a substrate 21 having an underlying layer 23, thereby obtaining a photoresist pattern 25. Then, a SAFIER material 27 is coated on the whole surface of the photoresist, and a thermal process is performed on the resulting structure. As a result, the photoresist material is shrunk 29 to form the photoresist pattern 25-1 reduced a size of a contact hole or a pattern.
Although the processes employing the RELACS material or the SAFIER material can reduce the size of the pattern regardless of a duty ratio, they are more costly and residuals remain in the pattern due to the incomplete removal of the water-soluble polymer, which adversely affects subsequent etching processes. As a result, defects are generated in the final devices, which degrades yield and reliability of the devices.
Moreover, since the above-described methods further include a coating process, a thermal process, a developing process, and a wafer cleaning process of two steps, the procedure is more complicated, and the process cost increases.